1. 2000-2001: DECIDING ON A DIGITAL AERIAL CAMERA

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1.1 Why Start a Camera R&D Project?

Vexcel Imaging GmbH in Graz (Austria, founded 1993) initially manufactured, marketed and sold over 400 photogrammetric film scanning systems UltraScan5000 from 1999 to 2005. By 2000 financial resources existed to add new products. At the ISPRS Congress (Amsterdam) first digital aerial mapping cameras with a large format were announced. Scrutiny of these products and an assessment of opportunities from all-digital photogrammetry were the basis for deciding in favor of developing a digital camera.

 

1.2 Assessing the 2000-Technologies

A review of patent applications reveals a plethora of ideas about digital photogrammetric imaging systems. We want to consider only technologies capable of producing “large format” images to replace photogrammetric aerial film.

 

The Leica ADS is a tri-linear scanning system analogous to the proposal by Derenyi (1970; see also Konecny, 1970), then describing a film based strip camera, and later implemented in a digital format by the German Aerospace Agency DLR (Neukum et al., 2001). Leica had purchased that technology. The initial product description was by Sandau et al. (2000), then Fricker (2001). Limitations were (i) much increased costs vis-à-vis film cameras, (ii) abandonment of the frame photograph and thus of the familiar workflows, (iii) uncertainty about achieving a photogrammetric accuracy at 1/10th of a pixel, and perhaps (iv) constraining data acquisition to a mere 3 images per terrain point and foregoing the opportunity of high overlaps and redundancy.

 

The Zeiss-Intergraph DMC produced a large image format by assembling 4 separate image tiles that get imaged simultaneously through 4 separate optical cones and merged by software.  This preserves the frame photo paradigm and thus the traditional photogrammetry workflows. Hinz et al. (2000 and 2001) described the approach and it was quickly evident that (i) it lacked software leverage and thus needed high cost of goods; (ii) the geometry relied on mechanical stability, not on redundancy and overlaps; (iii) the radiometric performance would suffer from a limited analog-to-digital conversion and high pan-sharpening ratio.

 

The INPHO ISPRS-2000 Camera was presented at the ISPRS-2000 congress with little technical detail, except for a patent reference to Teuchert & Mayr (2000). This development was abandoned in 2001. From it emerged a European multi-entity CONPIE GmbH under INPHO-leadership (Mayr & Ohlhoff, 2004). A product never materialized.

 

Thus only two vendors offered large format digital aerial systems, yet deliveries were delayed https://ad....nload.html. Computer technology still was bulky for very high in-flight data-rates and for operating reliably on non-pressurized survey airplanes. The collected data sets seemed forbiddingly large for space- and resource-constrained survey operations both in the air and in small photogrammetry offices.

 

1.3 Inventing a Novel Technology

Vexcel found it worthwhile to search for a novel digital large format camera concept that would (i) produce images as similar to scanned aerial film as possible, (ii) offer software leverage to support an end user price not higher than the traditional film cameras [thus at half the price for competing systems] and (iii) assure geometric and radiometric excellence by clever design rather than mechanical expenses. The search was successful, patent protection was applied for in May 2001 and a first employee started full-time on the UltraCam-project in September 2001. The basic imaging principle is illustrated in Figures 1 and 2 and various publications (Leberl et al., 2003, 2005; Gruber & Leberl, 2005, 2010; Gruber et al., 2003, 2008, 2012; Leberl & Gruber, 2003; 2005 a, b; Wiechert et al., 2011).

 

 

Figure 1:

The core idea of the UltraCam-technology is the assembly of one large aerial image from 9 separate tiles imaged through 4 separate optical cones numbered 1 through 4 [at right]. At left is a view of the 4 linearly arranged optical cones for the high resolution panchromatic image segments and the 4 additional optical cones for the lower resolution color channels. The resulting large format image has 5 bands with pan-infrared-red-green-blue. The pixel numbers at right concern the UltraCam-Xp model with 17.3K x 11.3K.

 

 

Figure 2:

Stitching image segments into one large image is a core skill being accomplished by one of two approaches. Above is the initial assembly based on the overlaps within the 4 separate panchromatic image segments. Below is a simultaneous adjustment of all image tiles using their overlaps as well as the green color-channel. A complex consideration concerns the effects of temperature on the deformation of the individual cones. Key publications about stitching are by Gruber & Ladstädter (2006, 2012) and Ladstädter et al. (2010)